feat: [Orchestration] Support Fallback Modules

[Jonas-Isr]

Context

AI/ai-sdk-java-backlog#342

This PR introduces support for using fallback modules when using orchestration chat completion. Instead of a single OrchestrationModuleConfig object, users can now add multiple of these module configs to a chat completion call (streaming or non-streaming). The configs are tried in the order they are given and if a call with a config failed, the next in line is used as fallback.

This PR also introduces a convenience layer to do this:

var prompt = new OrchestrationPrompt("your prompt");

var workingConfig = new OrchestrationModuleConfig().withLlmConfig(GPT_4O_MINI);
var secondWorkingConfig = new OrchestrationModuleConfig().withLlmConfig(GPT_4O);
var brokenConfig =
    new OrchestrationModuleConfig()
        .withLlmConfig(new OrchestrationAiModel("broken_name", Map.of(), "latest"));

var fallbackConfigs = new OrchestrationModuleConfig[] {workingConfig, secondWorkingConfig};

OrchestrationChatResponse result = client.chatCompletion(prompt, brokenConfig, fallbackConfigs);
// or:
// OrchestrationChatResponse result = client.chatCompletion(prompt, brokenConfig, workingConfig, secondWorkingConfig);

In the above example, the call with brokenConfig will return an error so another call with workingConfig is performed and the (positive) result of this call is returned.

Feature scope:

• test low-level code
• add convenience layer
• unit and e2e tests

Definition of Done

• Functionality scope stated & covered
• Tests cover the scope above
• Error handling created / updated & covered by the tests above
• Aligned changes with the JavaScript SDK
• Documentation updated
  • Java: Orchestration Fallback Modules ai-sdk#377
• Release notes updated

[Jonas-Isr]

The stream options are taken from the first config only. (I don't think there is a way to change this.)

[newtork]

(Major)

I think we can't allow for empty array chatCompletion(prompt) right?

[Jonas-Isr]

Eieiei, you are right! I fixed it :)